1. Technical Field of the Invention
The present invention relates to information processing and transmission in optical communication systems, and more specifically, it relates to techniques for increasing the switching and modulation speed of vertical-cavity surface-emitting lasers (VCSELs).
2. Description of the Prior Art
The limit to switching and modulation speed of semiconductor lasers is a fundamental bottleneck for information processing and transmission in optical communication systems. This limit comes from the relatively slow carrier recombination lifetime in the III-V semiconductors used for optical applications. Though progress in pushing this limit in the past has been made, these improvements cannot meet the demand for higher speed in the long run. A new paradigm has to be explored to maintain the momentum of technology development.
The ability to steer or switch propagation direction of a laser beam in a controllable way is very important for many applications, and especially for optical interconnect networks. Beam scanning and steering in edge emitting lasers have been realized using thermal control (See Y. Sun, C. G. Fanning, S. A. Biellak, and A. E. Siegman, IEEE Photonics Technol. Lett. 7,26(1995)) and spatial phase controlling techniques (See J. P. Hohim, D. C. Craft, G. A. Vawter, and D. R. Myers, Appl. Phys. Lett. 58, 2886 (1991)). For optical interconnect applications, all the well-known advantageous attributes of vertical-cavity surface-emitting lasers (VCSELs) make them especially appealing elements. However, full advantage cannot be taken of compact two-dimensional (2D) VCSEL arrays if bulky external passive optical elements are used for routing and switching, For this reason, routers integrated together with VCSELs that can be controlled electronically are especially important to reduce the overall volume of an interconnect network. See L. Fan, M. C. Wu, and P. Gradzinski, Electron. Lett. 31, 729 (1995) and L. Fan, M. C. Wu, H. C. Lee, and P. Grodzinski, IEEE Photonics Technol. Left. 9, 505(1997).
Recently, it has been demonstrate that, by introducing a phase-shifter in part of the VCSEL cross-section, beam switching up to 2 gigahertz can be achieved. Another more conventional approach to VCSEL beam manipulation is to use coherently coupled VCSEL arrays. Indeed VCSEL arrays of various kinds have been quite extensively researched for tailoring and engineering near and far field patterns. See M. Orenstein and T. Fishman, “Supermodes of Hermite Tapered Arrays of Vertical-Cavity Semiconductor Lasers,” IEEE J. Quantum Electron 35 1062-1066, (1999). See D. Natan, M. Margalit and M. Orenstein, “Loca;lization immunity And Coherence Of Extended Two-Dimensional Semiconductor Vertical Cavity-Locked Laser Arrays,” J. Opt Soc. Am. B 14, 1501-1504, (1997). See T. Fishman and M. Orenstein, “Cyclic Vertical Cavity Semiconductor Laser Arrays With Odd Numbers Of Elements: Lasing Modes And Symmetry Breaking.” Opt. Lett. 21 600-602, (1996)
It is therefore desirable to provide techniques for increasing the switching and modulation speed of semiconductor lasers for use in applications such as information processing and transmission in optical communication systems.